Method for filtering benz-a-anthracene from a gas stream

ABSTRACT

The present invention relates to a method of filtering, at the end user&#39;s home, business or the like, a gas stream in which benz-a-anthracene has been concentrated at sufficient levels to be a significant health hazard. Steps of the invention include: 
     (a) introducing the natural gas stream to a filter selected from a group that includes at least activated charcoal and impingement adsorbing media whereby benz-a-anthracene concentrated in the gas stream at sufficient levels to be a health threat by a periodic loading of such network in which benz-a-anthracene become clumped into packets due to dampening effects of the compressor-driven equipment and multiple customer outlet usage coupled with surprising longivity of the in situ benz-a-anthracene, is filtered from the gas stream and captured irrespective of mode of transport, 
     (b) passing the filtered natural gas stream to the customer&#39;s gas appliance wherein safe use of the energy associated with the stream occurs, 
     (c) periodically and safely removing the filter of step (a) for disposing of captured benz-a-anthracene, 
     (d) inserting a new filter in place of the removed filter of step (c).

SCOPE OF THE INVENTION

The present invention relates to a method of filtering. Moreparticularly, it relates to a filtering method to eliminatebenz-a-anthracene that had been concentrated within a conventional gasline network at sufficient levels to be a health threat. As a furtherconstraint, the sources of such benz-a-anthracene concentration areidentified. It is believed they result from aperiodic loading of suchnetwork in which benz-a-anthracene become clumped into packets due todampening effects of the compressor driven network and multiple customeroutlet usage that adds the aforementioned aperiodic loading within thenetwork.

DEFINITIONS

In the Application, "natural gas" means a mixture of gases associatedwith hydrocarbon accumulation within the earth as well as processed fuelgases derived from petroleum as well as mineral products such as coal ineither gas or liquid phases. In some gas line networks, the resultingfinal gases may be a mixture from these two sources but wherein theessential component consists of methane.

"Sufficient level to be a health threat" means a recognized standard forhuman health and safety established by authoritative bodies above whichcancer or reproductive toxicity in humans results, such bodies toinclude but not be limited to the U.S. Environmental Protection Agency(EPA), the U.S. Department of Food and Drug Administration (FDA) and theU.S. Department of Commerce. The EPA has set health and safety standardsfor radon which, if exceeded, would pose a risk to human health.

"Adsorption" means filter media that captures molecules of a gas, liquidor dissolved substance to the filter surface, by adhesion.

"Absorption" means filter media that absorbs molecules of a gas, liquidor dissolved substance to the filter itself, by taking in through poresor interstices.

"Impingement" means filter media that captures molecules of a gas,liquid, solid or a dissolved substance to the filter by physical capturesuch as by change in velocity.

BACKGROUND OF THE INVENTION

The danger of benz-a-anthracene is well documented. Benz-a-anthraceneconcentration levels at a customer-end user's home, business and thelike are not monitored, however. Believed to cause cancer, skin andorgan damage and bone marrow depression, benz-a-anthracene has acutepenetration efficiency and once within a human's body, does notdissipate and builds a significant body burden as a function offrequency and level of exposure. While the EPA and various StateAgencies may be aware of the problem of benz-a-anthracene in gas lines,they do not think the reported exposure is of sufficient levels to bedangerous.

In such situation, I find that surprisingly large concentrations ofbenz-a-anthracene sporadically occur. Sources of such concentration:dampening effects of the compressor-driven network and multiple customeroutlet usage that add to aperiodic loading of the natural gas streamcoupled with surprising longevity of the in situ benz-a-anthracene. As aresult, benz-a-anthracene can flow to appliances in the customer's home,business or the like at sufficient levels to be a health hazard, i.e.exceed Federal and/or State health and safety standards. Moreover,although the original source of the benz-a-anthracene is in the gasphase, both liquid and gaseous forms can be transported alone or attachto particulates and form the final end-use contamination levels at theappliance to be used.

SUMMARY OF THE INVENTION

The present invention relates to a method of filtering, adjacent to theend user's home, business or the like such as the adjacent gasdistribution and processing system connected to the end user's meter, agas stream in which benz-a-anthracene has been concentrated atsufficient levels to be a significant health hazard. Steps of theinvention include:

(a) introducing the natural gas steam to a filter selected from a groupthat includes at least activated charcoal and impingement adsorbing andabsorbing media whereby benz-a-anthracene concentrated in the gas streamat sufficient levels to be a health threat by aperiodic loading of suchnetwork in which benz-a-anthracene become clumped into packets due todampening effects of the compressor-driven equipment and multiplecustomer outlet usage that add to aperiodic loading of the natural gasstream coupled with surprising longevity of the in situbenz-a-anthracene, is filtered from the gas stream and captured.

(b) passing the filtered natural gas stream to the customer's gasappliance wherein safe use of the energy associated with the streamoccurs,

(c) periodically and safely removing the filter of step (a) fordisposing of the captured benz-a-anthracene,

(d) inserting a new filter in place of the removed filter of step (c).

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a gas valve-meter assembly attached at oneend to a pipe of a gas line network adjacent to a home, business or thelike, along with a filtering assembly and by-pass network of the presentinvention;

FIG. 2 is a top view of the filtering assembly of the invention;

FIG. 3 is a section taken along lines 3--3 of FIG. 2;

FIG. 4 is an enlarged detail view taken along lines 4--4 of FIG. 3;

FIG. 5 is an enlarged detail of the filter media unit of FIG. 3;

FIG. 6 is an enlarged detail of an insert ring used in the filter mediaunit of FIG. 3; and

FIG. 7 is an alternate design for the filter unit of FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a gas meter 10 connected via elbow 11 and gas pipe 12to a main gas line network (not shown). Downstream of the meter 10 is atee coupler 14 having a first end 15 connected to an overhead by-passnetwork generally indicated at 16, and a second end 17 connected througha first valve 18 and inlet fitting 19 to filter assembly 20. The filterassembly 20 in turn connects via outlet fitting 40, elbow 41 and asecond valve 42 to the overhead by-pass network 16. As shown, theby-pass network 16 includes a parallel by-pass valve 43. In operation,the by-pass valve 43 operates in complementary fashion with respect tofirst and second valves 18 and 42, respectively. When valve 43 isclosed, as shown, the valves 18 and 42 are open and the filter assembly20 is in operation. When valve 43 is open, the valves 18 and 42 areclosed and the filter assembly 20 is in a deactivated state.

FIGS. 2, 3 and 4 show the filter assembly 20 in more detail.

As shown, the filter assembly 20 includes a cap 21 fitted with arectangularly cross-sectioned dome 22 at its upper surface 21a, seeFIGS. 2 and 4, to which the pipe fittings 19 and 40 attach. The cap 21also has a lower surface 21b fitted with nipples 23 adjacent to a seriesof passageways that allow entry and egress of the gas stream: (i) inletpassageway 24 is L-shaped, is threadably connected to the inlet fitting19 at one end, and is also connected via central annulus 25 to interiorfilter media unit 26 concentric of vertical axis of symmetry 27; (ii) anoutlet passageway 28 that is bulbous over region 29 but is in fluidcontact with annular gathering region 30 that runs the full exterior ofthe filter media unit 26; the passageway 28 is then swedged over region31 (in a L-shaped output form) at one end of bulbous region 29 forconnection to outlet fitting 40.

The cap 21 also has an annular side wall 21a, see FIG. 4, and inwardlyswedged at shoulder 32 and terminates at end 33. It is threadedtherebetween to engage with cylindrical canister 34. The canister 34includes a side wall 34a offset from the filter media unit 26 to formthe annular gathering region 30 previously described and in addition,has shoulders 35 and 36. The region between the shoulders 35, 36 and isthreaded to engage cap 21. Between shoulders 32 and 35 of the cap 21 andcanister 34, respectively, is grooved O-ring 37 to prevent gas leakageexterior of the filter assembly 20. The length of the engaging threadedportions of the cap 21 and canister 34 are constructed so that positivecontact exists only at the O-ring 37 and not at shoulders 33, 36.

Canister 34 also includes a bottom wall 34b. The bottom wall 34bincludes upwardly projecting nipples 38 concentric of a central annulus39. The latter attach to the filter housing 26. The purpose of thenipples 23 and central annulus 25 of the cap 21 as well as that of thenipples 38 and central annulus 39 of the canister 34 is to fixedlyreceive and hold the filter media unit 26 relative to the cap 21 andcanister 34.

Note that the direction of the gas stream at the interior of the filterassembly 20 is as taught by arrows 45, see FIG. 4. Such gas streamcannot pass directly from inlet passageway 24 to outlet passageway 28but is prevented to such flow due to the length of the annuli 25, 39.Thus the gas flow is in a radially expanding, sinusoidal pattern normalto the axis of symmetry 27 about horizontal axis A--A of the filtermedia unit 26. The pattern begins at the axis of symmetry 27 andprogresses through filter media unit 26, and ends exterior of the latterat annular gathering region 30. Thus the benz-a-anthracene is filteredfrom the stream.

FIG. 5 illustrates filter media unit 26 in more detail.

As shown, the filter media unit 26 includes end pieces 50a, 50b eachhaving a circular notch 51 at outer surface 52 into which nipples 23, 38of the cap 21 and canister 34, respectively, are received. Suchconstruction permits the end pieces 50a, 50b to take up firm surfacecontact with the cap 21 and the canister 34 as the cap 21 is threaded tothe latter.

Interior of the end pieces 50a, 50b are a series of concentric tubes 53,54, 55, 56 and 57 fitted into the notches 51 of the former. The tubes53-57 have side walls fitted with performations 59. The side walls arenormal to the horizontal axis of symmetry A--A previously mentioned, thelatter being also normal to the vertical axis of symmetry 27. Theperforations 59 permit gas flow in the sinusoidal-like, single passfiltering manner relative to axis A--A within the tubes 53-57 asindicated by arrows 45. As shown these arrows 45 begin near the verticalaxis of symmetry 27 and serpentine outwardly in sinusoidal fashionthrough the filter media unit 26.

Note that between the tubes 53 and 54; between tubes 54 and 55; betweentubes 55 and 56 and between tubes 56 and 57 are separate filter medium60, 61, 62 and 63 together forming a four-stage, single pass filteringmedia which in combination remove all benz-a-anthracene from the gasstream. The media 60-63 are each selected to remove benz-a-anthracenefrom the gas stream in progressive fashion, viz., from microscopic tomillimicrospic levels via single passage of the gas stream through eachmedium 60-63. However, the media 60-63 do not filter the methane fromthe gas stream.

FILTER MEDIUM 60

In this regard, filter medium 60 is preferably pleated filter paperhaving the following characteristics. Pleated filter paper 60 is widelyavailable, performs impingement, absorption and adsorption and is madeby conventional manufacturing processes including but not limited tomethods involving weaving of cellulose, wool, acrylic, rayon fibers intocorrugated sheet form. The tips and troughs of the corrugated pleatedfilter paper 60 of FIG. 5 are located in accordion fashion across andwithin the tubes 53, 54 but not in contact with the upper and lower endpieces 50a, 50b of the filter media unit. As shown in FIGS. 5 and 6, aseparate ring 64 is fitted in contact with each end piece 50a, 50b. Thering 64 of rectangular cross section, includes side wall 66 andterminating broad surface 67, that is compressively fitted in snugcontact with the upper or lower end piece 50a, 50b. As a result, the gasstream can circulate in the manner shown and pass through the pleatedfilter paper 60 in single pass fashion between inlet and outletperforations 59 associated therewith.

The density of paper 60 varies to provide filtering of benz-a-anthracenecarried on dust, rust, dirt, moisture and oil laden particles in a rangeof 40 to 750 microns. It also retains both oils and moisture.

FILTER MEDIUM 61

In this regard, filter medium 61 is preferably silica gel in crystallineform located between tubes 54 and 55.

Silica gel 61 is a conventional drying and dehumidifying agent formed ofamorphous silica in crystalline form for filtering and trappingbenz-a-anthracene transported in solution with water, in gaseous form aswell as aboard smaller diametered dirt and dust particles carryingbenz-a-anthracene piggyback. The gel absorbs moisture within the gasstream but not oils and is located between tubes 54 and 55. The medium61 provides for single passage filtering operations only.

Calculations associated with the above are as follows:

AVERAGE NATURAL GAS USAGE

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Assume the area between tubes 54, 55 is a function of a mean diameter of35/8 inches, a height of 5 inches and thickness of 0.875 inches, then

    Filter volume=52.5 cu. inches.

FILTER MEDIUM 62

Filter medium 62 is preferably open pore polyurethane foam for capturingbenz-a-anthracene is gaseous form. Filter medium 62 filters byimpingement and adsorption and retains micro vapors and solidparticulates including oils and is located between tubes 55 and 56 forsingle pass filtering operations. It has the following characteristics.

Shape: Cylindrical shape from sheet form

Cellular Matrix Structure

Medium density--0.1 to 0.4 g/cu. cm matrix solid foam to gas insert

Porosity--0.14 to 0.41 (i.e. 70% to 90% open pore polyurethane)

Sample Period--2 months AT 100% Retention

Well below breakthrough volume, viz., the point at which concentrationof solute in the column effluent is half the concentration introducedinto the column.

Volatility--Medium, See below

Preparation--Cut from foam sheets; air dry; install.

Pressure Drop--0.015 psi

Calculations associated with the above are as follows:

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

where: 0.0364 micro g/cu. meter per meter is benz-a-anthracene;

Hence: 295 cu.meter/month produces 10.738 micro g/mo ofbenz-a-anthracene;

And: 0.0027612 cu. cm required to remove above am't of benz-a-anthracene

Filter volume=408.28 cu. cm via 5 inches height by 1/2 inches thicknessby 15.7 inches long;

Efficiency--700 cu. meters available

Change frequency=well within above pattern

FILTER MEDIUM 63

Furthermore, filter medium 63 is preferably granular activated charcoallocated between tubes 56 and 57 for single pass filtering operations.

Granular activated charcoal is a conventional filtering medium, performsfiltering on liquids, gases and solid particulates down to 10 Angstromsin size (but does not retain water) by impingement and adsorption and isprepared by carbonization of raw materials such as wood, coconut shelland coal. It attracts and holds benzene irrespective of the mode oftransport such as a liquid or gas alone or piggyback aboard dirt anddust particles as well as with liquid plugs.

Physical properties:

Surface Area=600 to 1050 cubic meters per gm

Density=0.92 to 2.0 grams per cubic meter

Effective size=0.8 to 1.5 mm

Pore volume=0.6 to 1.7 cubic cm per gram

Mean diameter=1.2 to 1.7 mm

Sieve Size=No. 8 to No. 40 (U.S. Series)

Iodine No.=650 to 1,000

Calculations associated with the above are as follows:

Assume average gas use is 125 MSCF/YR, then per month usage cubic metersis

    125 mcf/yr/12=10,416.6 cu. ft/month/35.3=295 cu. meters/month

Assume the area between tubes 54, 55 is a function of a diameter of 7inches, a height of 5 inches and a thickness of 0.5 inches, then

Filter volume=55. cu. inches;

Density of GAC=0.30 oz./cu. in

GAC Aviail=16.5 oz.

Requirement to remove benz-a-anthracene associated with 295 cu. metersis well within above change pattern.

FIG. 7 illustrates alternate filter media unit 69 in detail.

As shown, the filter media unit 69 is similar to the filter media unit26 previously described, such filter media unit 69 having end pieces 70,71 fitted with inwardly facing notches 72 (relative to a horizontal axisof symmetry, not shown), and a series of concentric tubes 73, 74, 75, 76and 77 collinear with axis of symmetry 78. However, perforations 79 areprovided in side walls of tubes 73-77 to allow radial flow outwardlyfrom vertical axis of symmetry 72. Such construction does not permit thesinusoidal flow as previously mentioned, however. Instead, a gas streamflows as an annular mass through the filter media unit 69 beginning atthe axis of symmetry 78 and ending at the exterior of tube 77. Suchpattern is indicated by arrows S that are seen to expand outwardly fromthe axis of symmetry 78. The notches 72 aid in assembly as they take upfirm surface contact with the cap 21 and canister 34 of FIGS. 2, 3 and4, as the former and latter are threaded together.

Between the tubes 73 and 74; between tubes 74 and 75; between tubes 75and 76, and between tubes 76 and 77 are separate filter medium 80, 81,82 and 83 together forming a four-stage filtering media which incombination remove benz-a-anthracene from the gas stream. That is, themedia 80, 81, 82 and 83 are selected to remove all traces ofbenz-a-anthracene from the gas stream in the same order and similarfiltering capacity as previously discussed with reference to FIG. 5. Inthis regard, filter medium 80 is pleated paper, medium 81 is silica gel,medium 82 is open pore polyurethane foam and medium 83 is granularactivated charcoal each having characteristics as set forth above.

GUIDELINES FOR SELECTION OF FILTER MEDIA 60-63 & 80-83

Benzene exists in two states within the gas line network: primarily as aliquid and as a vapor. It is carried along because of the pulsation ofthe gas stream and surprisingly because of the gas phase transitioneffects created by the drive compressors of the gas system augmented bythe multiple outlet demands of the customers. But no matter how thebenz-a-anthracene is carried in the gas stream, the former are trappedwithin the filter media 60-63 and 80-83 of the invention.

Gas phase transition is a little understood phenomenon in which variousdynamics due to changes in temperature, pressure, pipe size, flow ratesthat cause interaction between hazardous elements of the gas stream andvarious other elements in the network, such as pipe coatings, plug flows(aggregations of materials moving as a group) liquids and gaseous phasesof constituents of the natural gas stream. As a result, liquids andgases within the natural gas stream surprisingly change state. Theresulting gaseous phase may contain the hazardous elements which aretransported great distances.

As a vapor or liquid, the benz-a-anthracene is then carried along underlike sets of circumstances described above.

PRESSURE CONDITIONS

As surface residue on solid particulates, benz-a-anthracene is carriedalong as follows. At the well site, pressures in access of 2,000 psioccur. Such pressure can be maintained until stepped down to about 1,000psi, thence to 60 psi and finally to about 1/2 psi at the user'sresidence or business.

While filter media 60-63 and 80-83 are preferably as discussed above,substitutions can be made. For example, other types ofimpingement-adsorbing media could be used including silica sand,activated clay such as montomorillanite, natural zeolites composed ofhydrous calcium and aluminum silaceous materials, synthetic zeolitescalled molecular sieves such as sodium aluminum silicates, caitlin siltloam, dried corn husks, etc. Also, fluid baths, sonic collectors,electrostatic precipitators and thermal de-humidification devices couldalso be used.

Other impingement adsorbing media includes other packings such as can bewoven, coated or impregnated (such as with glycerol, glycerin, oils,glycol etc.). Other types of filters include membrane filter media foruse in natural gas environments generally above 100 psi in which thesolute is the force that helps perform the filtering, as well as specialfilters such as elongated, inter-latticed baffles that provideelectrostatic collection such as the HEPA filter (High EfficiencyParticle Accumulator filter, an acronym of The National Aeronautics andSpace Administration).

In some applications, fluid baths could be used, in which fluidsselected from a group that includes water, oil, alcohol, glycerol,glycerin, and glycol, could be used. Such use would require amodification to the canister 34 in order to provide a filteringoperation.

FURTHER METHOD ASPECTS

After installation has occurred, the filter system is an activefiltering state for benz-a-anthracene. That is to say, the valve 43 inthe by-pass network 16 is closed and the valves 18 and 42 upstream anddownstream of the filtering assembly 20 are opened.

When the filtering assembly 20 is to be re-charged, the valve 43 in theby-pass network 16 is opened so that gas is passing in parallel to thedownstream appliances (not shown). This assures ample gas supply beforethe filtering assembly 20 is deactivated. Such deactivation occurs whenthe valves 18 and 42 are closed. Then the canister 34 with the filtermedia 60-63 & 80-83 captured within its side wall 31, is removed fromcontact with cap 21, and the canister 34 and filter media 60-63 & 80-83are removed for transport to a waste station and disposal. A newcanister 34 with new filter media 60-63 or 80-83 are re-attached.

The above description contains several specific embodiments of theinvention. It is not intended that such be construed as limitations onthe scope of the invention, but merely as examples of preferredembodiments. Persons skilled in the art can envision other obviouspossible variations within the scope of the description. For example,the filter assembly 20 can be inserted in higher pressure lines of thegas transfer network, such as within the local utilities' pipingnetwork. Hence the scope of the invention is to be determined by theappended claims and their legal equivalents.

What is claimed is:
 1. A method of filtering, adjacent to an enduser-customer's residence or business in which at least a single gasapplicance is located, a natural gas stream in which benz-a-anthracenehas been concentrated at sufficient levels to be a health threat in anatural gas gathering and distributing network, comprising the stepsof:(a) introducing the natural gas stream to a filter selected from agroup that includes impingement, absorbing and adsorbing media wherebybenz-a-anthracene concentrated in the gas stream at sufficient levels tobe a health threat by aperiodic loading of the natural gas within thegathering and distributing network, are filtered from the gas stream andcaptured irrespective of mode of transport, (b) passing the filterednatural gas stream to the customer's gas appliance wherein safe use ofthe energy associated with the stream occurs, (c) periodically andsafely removing the filter of step (a) for disposing of capturedbenz-a-anthracene, (d) inserting a new filter in place of the removedfilter of step (c).
 2. The method of claim 1 in which said impingement,absorbing and adsorbing media of step (a) for filteringbenz-a-antahracene, are selected from the group comprising pleatedfilter paper, silica gel, open pore polyurethane foam and granularactivated charcoal.
 3. The method of claim 2 in which said impingement,absorbing and adsorbing media of step (a) comprises in seriatim, pleatedfilter paper, silica gel, open pore polyurethane foam and granularactivated charcoal whereby benz-a-anthracene is removed from the naturalgas stream.
 4. The method of claim 1 in which step (a) is furthercharacterized by aperiodic loading of in situ benz-a-anthracene beingthe result of gas phase transition effects occurring within the naturalgas gathering and distribution network.
 5. The method of claim 4 inwhich step (a) is further characterized by the natural gas gathering anddistributing network including compressor-driven equipment and multiplecustomer outlets connected to such equipment and by aperiodic loading ofin situ benz-a-anthracene within the natural gas gathering anddistributing network being the result of dampening effects of thecompressor-driven equipment and multiple customer outlet usage.
 6. Themethod of claim 5 in which the natural gas gathering and distributingnetwork includes gas meters each connected to one of the outlets of thenetwork and wherein said filtering occurs after such gas stream exitsfrom the end user's gas meter.
 7. The method of claim 1 in which saidfiltering occurs in the natural gas gathering and distributing network.8. A method of filtering adjacent to an end-user-customer's residence orbusiness in which at least a single gas appliance is located, a naturalgas stream in which benz-a-anthracene has been concentrated atsufficient levels to be a health threat within a natural gas gatheringand distributing network connected to the customer's gas appliancecomprising the steps of:(a) introducing the natural gas stream to afilter selected from a group that includes impingement, absorbing andadsorbing media whereby benz-a-anthracene concentrated in the gas streamat sufficient levels to be a health threat due to aperiodic loadingwithin the natural gas gathering and distributing network, is filteredfrom the gas stream and captured irrespective of mode of transport, (b)passing the filtered natural gas stream to the customer's gas appliancewherein safe use of the energy associated with the stream occurs.
 9. Themethod of claim 8 with the additional steps of:(c) periodically andsafely removing the filter of step (a) for disposing of capturedbenz-a-anthracene, (d) inserting a new filter in place of the removedfilter of step (c).
 10. The method of claim 8 in which said impingement,absorbing and adsorbing media of step (a) for filteringbenz-a-anthracene is selected from the group comprising pleated filterpaper, silica gel, open pore polyurethane foam and granular activatedcharcoal.
 11. The method of claim 10 in which said impingement,absorbing and adsorbing media of step (a) comprises in seriatim, pleatedfilter paper, silica gel, open pore polyurethane foam and granularactivated charcoal whereby benz-a-anthracene is removed from the naturalgas stream irrespective of mode of transport.
 12. The method of claim 8in which step (a) is further characterized by aperiodic loading of insitu benz-a-anthracene being the result of gas phase transitionaleffects occuring within the natural gas gathering and distributingnetwork.
 13. The method of claim 12 in which step (a) is furthercharacterized by the natural gas gathering and distributing networkincluding compressor-driven equipment and multiple customer outletsoperationally connected to such equipment and wherein step (a) is alsocharacterized by clumping of in situ benz-a-anthracene that is theresult of dampening effects produced by the compressor-driven equipementand multiple customer outlet usage within the natural gas gathering anddistributing network.
 14. The method of claim 13 in which the naturalgas gathering and distributing network includes gas meters eachconnected to one of the outlets of the network and wherein steps (a),(c) and (d) occur after the natural gas stream exits from the end user'sgas meter.
 15. The method of claim 13 in which steps (a), (c) and (d)occur within the natural gas gathering and distribution network.